In this study, we evaluated the antileukemic activity of lintuzumab-Ac225 in FLT3 mutant AML as a single agent and in combination with the FLT3-targeted inhibitor gilteritinib….Treatment of MV-4-11 cells with lintuzumab-Ac225 resulted in a dose-dependent reduction of cell viability within 48 hours which was significantly more potent relative to non-labeled lintuzumab or gilteritinib alone. The combination of lintuzumab-Ac225 with gilteritinib further reduced cell viability relative to relative to single agents at the dose levels studied…. Our findings show that single-agent lintuzumab-Ac225 has potent antileukemic activity against FLT3 mutant AML and can significantly improve the effect of FLT3 inhibitors in combination.